Studies On The Supported Nickel Catalysts For The Hydrogentaion Of α-Pinene

Supported nickel catalyst is of the most important catalysts for hydrogenation reaction. In this work, the dispersion state of NiO, the interaction between dispersed nickel species andγ-Al₂O₃ support, and the catalytic properties of supported Ni/γ-Al₂O₃ catalysts for hydrogenation ofα-pinene have been studied by using various phyico-chemical techniques combined with micro-reactor tests. The effect of La₂O₃ , CuO promoters and the mesoporous structure of catalyst support on the catalytic properties of supported Ni catalysts have been studied as well.The dispersion capacity of NiO onγ-Al₂O₃ measured by XRD is almost identical to the value calculated from the"Incorporation Model", suggesting that the highly dispersed nickel ions locates on octahedral and tetrahedral vacancies ofγ- Al₂O₃ preferentially exposed (110) plane. When NiO loading is far below its dispersion capacity onγ- Al₂O₃, nickel ions preferentially incorporate into the tetrahedral vacancies. With increasing NiO loading, the ratio of Ni2+ that incorporate into octahedral vacancies increase.When NiO loading is beyond its dispersion capacity, crystalline NiO appears onγ- Al₂O₃.It has been found that the octahedral Ni2+ ions are easier to reduce to metallic Ni0 than tetrahedral Ni2+, and thus the catalytic activity of Ni/γ- Al₂O₃ catalyst for hydrogenation ofα-pinene greatly increase with Ni loading. By adding La₂O₃ component to NiO/γ- Al₂O₃ sample, the ratio of Ni2+ ions incorporated into octahedral vacancies increase, the catalytic activity of Ni-La/γ- Al₂O₃ catalyst for hydrogenation ofα-pinene can be improved. On the other hand, by adding CuO component to NiO/γ- Al₂O₃ sample (Cu/Ni molaric ratio≤0.5), the ratio of Ni2+ ions incorporated intooctahedral vacancies decreases, and the catalytic activity of Ni/γ- Al₂O₃ catalyst decreases; When Cu/Ni molaric ratio is higher than 0.5, the activity of the catalyst can be improved not only because of the catalytic activity of Cu0 in Ni-Cu/γ- Al₂O₃ catalyst but also because of the Cu0 promotional effect to Ni2+ ions reduction.Moreover, the mesoporous material SBA-15 has been used as the support of Ni catalyst. It has been shown that the supported Ni/SBA-15 catalyst is more active than Ni/γ- Al₂O₃ catalyst for hydrogenation ofα-pinene, which suggests the Ni/SBA-15 catalyst is a potentially new catalyst for hydrogenation reactions.